1. Field of the Invention
This invention relates to a photochemical vapor deposition method, and more particularly to a novel process for producing a photochemical vapor deposition thin film by which a thin film of high purity can be formed at a low temperature using a photochemical reaction.
2. Description of the Prior Art
A photochemical vapor deposition apparatus (hereinafter abbreviated as PCVD apparatus) is an apparatus which includes a reaction chamber, a means for introducing starting gas into the reaction chamber and a means for irradiating the starting gas with a light of high energy and by which a thin film is deposited on a substrate placed in the reaction chamber by utilizing the photochemical reaction.
FIG. 1 shows a basic construction of a representative PCVD apparatus employed in the prior art. In FIG. 1, 1 is luminous flux, 2 a window, 3 a reaction chamber, 4 a valve for introducing starting gas, 5 a thin film, 6 a substrate, and 7 an outlet.
The conventional PCVD apparatus of this type can form a film by decomposing the starting gas by use of light energy. For example, there is known a process in which a silane gas introduced into reaction chamber 3 is irradiated with light of high energy such as excimer laser and the like to form a silicon hydride film on the substrate. In this process, since the film is formed only by use of light energy, there were defects that the deposition rate is low, the bonding between silicon atoms and hydrogen atoms does not sufficiently proceed and electrical properties of the film formed in insufficient.
For example, the reactions such as those mentioned below may be supposed as the possible reactions for forming silicon hydride by the decomposition of silane gas. EQU SiH.sub.4 *.fwdarw.Si*+2H.sub.2 EQU SiH.sub.4 *.fwdarw.SiH*+H.sub.2 +H
(* shows an excited state.)
However, energy needed for each dissociation reaction is different from each other. Therefore, it is difficult to treat all of these dissociation reactions only by a light having a single wavelength.